Newswise — Solar calendars and sun cults were an important part of indigenous American culture, from the Hopi to the Inca sun temple in Cusco, Peru. The latest issue of Science features a new discovery at Chankillo, in the Casma Valley of Peru's coastal desert, pushing sun cults in the region back nearly 2,000 years.

A line of structures known as the 13 towers run north-south along the ridge of a low hill at Chankillo, a ceremonial center dating back to the fourth century B.C. From evident observation points on either side, the towers form a "toothed" horizon that spans the annual rising and setting arcs of the sun, indicating their use in solar observations.

"Chankillo is arguably the oldest solar calendar that can be identified as such with confidence within the Americas," said Ivan Ghezzi (Pontificia Universidad Catolica del Peru), who coauthored the Science paper with Clive Ruggles (University of Leicester).

Starting in 2000, Earthwatch volunteer teams assisted Ghezzi at Chankillo for three years, conducting excavations that supported this new revelation about the site's importance in ancient sun cults. They assisted in mapping the 13 towers, recording their alignments, and excavating the "solar observatory" to the west. Earthwatch volunteers also took tree ring samples from well-preserved wooden lintels that helped date the site.

"Many indigenous American sites have been found to contain one or a few putative solar orientations," continued Ghezzi. "Chankillo, in contrast, provides a complete set of horizon markers and two unique and indisputable observation points."

Excavation of ancient buildings to the west of the towers revealed one corridor that was clearly an observation point for watching the sun rise over the toothed horizon. The end of the corridor was littered with offerings of pottery, shell, and stone artifacts not found elsewhere nearby, indicating significant rituals associated with solar observations. A building to the east is in the exact mirror position of the western observation point, and is lined up to view the sunsets over the 13 towers.

The gaps between the towers are wide enough for just one or two sunrises to be observed in each. The regularity of the gaps suggests that the year was divided into regular intervals.

Plazas near the 13 towers apparently provided a setting for people participating in public rituals and feasts directly linked to solar observations. However, the observation points themselves appear to have been highly restricted to individuals with special status. This, along with ceramic warrior figurines found at the site, suggest the authority of an elite few. As with the Inca empire, two millennia later, sun worship and cosmology may have helped legitimize that authority.

"Chankillo was built approximately 1700 years before the Incas began their expansion," said Ghezzi. "Although there is obviously no direct culture-historical relationship between the 13 Towers of Chankillo and the sun pillars of Cuzco, they are analogous as horizon markers for calendrical purposes. Now we know these practices are quite a bit older, and were highly developed by Chankillo's time."

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